1. Field of the Invention
This invention relates to the transfer of baseband digital data in a hospital environment, and, in particular, to a low cost, efficient, and reliable system for transferring such data among and between central processors and processors located at the beds of individual patients.
2. Description of the Prior Art
The increasing use of computers and microprocessors in hospitals has led to a need for efficient and effective means for transferring digital data between different locations in the hospital. In particular, there has developed a need for two-way digital communication with a patient in his bed over existing coaxial cables. Such communication can, for example, be used to remotely monitor the patient, to request and receive information from the patient, e.g., order entry from the patient's bed, daily menu selections, and the like, to control and monitor the patient's environment, e.g., room lighting, air conditioning, door release, bed controls, smoke detectors, and the like, and to control and monitor the entertainment services and prescription services available to and used by the patient, e.g., forced tuning of TV channels, remote readout of the TV channel being watched at the patient's location, TV channel lockout, adding or skipping of TV channels, and the like.
A possible approach for providing the desired data transfer capability at each patient's bed would be to use a dedicated pair of conductors for each bed. Although this approach might be practical for new hospitals and for some existing hospitals, it is obviously expensive and, for existing hospitals, installation would involve a major interruption of on-going hospital activities. Also, for many existing hospitals, there is insufficient space in existing electrical conduits to add additional wiring. Accordingly, for these hospitals, in addition to the basic wiring, more conduits would also have to be added.
In an attempt to deal with the wiring problem, efforts have been made to transmit digital data on the coaxial cable network which hospitals normally use to carry RF television signals to the television receivers at each patient's bed. This cable network has in the past been adapted to provide DC power to the patient's television set. See Bunting, U.S. Pat. No. 3,699,250.
The approach generally considered to date has been to add additional RF bands to the existing bands already on the cable to carry the digital data. See, for example, European Patent Publication No. 103,438. The inventors of the present invention have worked with this approach and have developed prototype systems employing such additional RF bands. Surprisingly, the added RF bands approach has been found to be significantly more expensive to implement in practice and less reliable in use than the baseband digital data transfer system of the present invention. Also, the RF approach was found to suffer more attenuation than the present system in conducting digital signals over long distances and to be less noise immune than the present system.
The use of frequency-coded and pulse-coded control signals, as well as DC control signals, to activate selected equipment or serve a "nurse call" function has been disclosed in various patents. For example, Friesen et al., U.S. Pat. No. 3,534,161, discloses the use of frequency-coding or pulse-coding to connect the audio portion of a patient's television to a nurse's station. Fay, U.S. Pat. No. 3,946,159, discloses a nurse call system using DC control voltages of different magnitudes. Bunting, U.S. Pat. No. 3,517,120, discloses a nurse call system using a 100 kilohertz control signal. See also Tanner, U.S. Pat. No. 3,492,418; Damoci, U.S. Pat. No. 4,630,313: and U.K. Patent Application Ser. No. 2,022,963.
Along these same lines, Bunting, Inc., the assignee of the present invention, has in the past used interruption of the flow of DC current in a coaxial cable leading to a patient's television set as a control signal for controlling, inter alia, the position of a patient's bed. See also Hempell, U.S. Pat. No. 4,443,815, which discloses a system for detecting tampering with a cable TV system by sensing an interruption of the DC path through the cable.
In the former Bunting system, a coaxial cable carrying RF television signals and DC power for the patient's television set was supplied to the patient's hospital room. The cable was passed through a decoder circuit which was designed to sense interruptions in the flow of DC current in the cable. The decoder circuit was connected to a relay bank which determined the position of the patient's bed. From the decoder circuit, the cable was passed through an encoding circuit which interrupted the flow of DC current through the cable a preselected number of times at a preselected rate depending on the bed position selected by the patient. Finally, the cable was connected to the patient's television set, where it provided RF signals and DC power.
In operation, the patient would press a button on his television set corresponding to the position he desired for his bed, the pressing of the button would cause the encoder to generate a series of DC current interruptions corresponding to the selected button, and the interruptions would cause the appropriate relays to be activated to move the bed into the position selected by the patient.
Significantly, with regard to the present invention, the foregoing systems were concerned with the communication of simple control signals, not with the two-way transmission of streams of digital data at high baud rates. In addition, none of these systems addressed the problem of distinguishing between data being received at a station and data being sent from that station.